单例模式

（1）不用装饰器实现

class MyClass2(object):
    __instance = None

    def __new__(cls, *args, **kwargs):
        if not cls.__instance:
            cls.__instance = object.__new__(cls)
        return cls.__instance


t1 = MyClass2()
t2 = MyClass2()
print(id(t1), id(t2))

 

（2）用装饰器实现

def decorate(func):
    instance = {}

    def fun(*args, **kwargs):
        if func not in instance:
            instance[func] = func(*args, **kwargs)
        return instance[func]

    return fun


@decorate
class MyClass3(object):

    def __init__(self, name):
        self.name = name


m1 = MyClass3("aa")
m2 = MyClass3("bb")
print(id(m1), id(m2))
print(m1.name)